This invention relates to a process for producing a resin-coated paper used as a photographic support and particularly a resin-coated paper of which coating is made by melt-extrusion of a polyolefin resin, as well as to an apparatus for producing said resin-coated paper.
As the support of photographic printing paper, polyolefin resin-coated paper has been mainly used up to today.
This type of resin-coated paper is produced by the so-called T die extrusion coating process which comprises extrusion-coating a molten resin onto a continuously running paper substrate. Photographic supports produced according to this process range from those having a basis weight of about 70 g/m.sup.2 used as printing paper of computer or pringing plate material to those having a basis weight of about 200 g/m.sup.2 used as color printing paper, and they are furnished in the form of a roll.
As a problem concerning the quality of rolled product, the phenomenon of "upheaval" on paper surface can be referred to. This phenomenon exercises a particularly marked influence upon resin-coated papers having a basis weight of about 70-150 g/m.sup.2, and this phenomenon makes an important trouble to photographic support. The upheaval phenomenon referred to herein is due to the minute defective profile in resin thickness in the direction of width which appears at the time of coating a molten resin. Even if this defect is negligible on a single sheet, the minute difference in thickness is accumulated on a roll, until it produces a so-called "iron hoop-like upheaval" on the circumference of a roll of resin coated paper. If a photographic emulsion is applied to resin-coated paper unrolled from such a roll having such an upheaval, unevenness appears in the emulsion coating and gloss and fogging and the like appear to deteriorate the photographic characteristics due to the difference in pressure, which results in making an important trouble.
Such an upheaval is caused not only by unsatisfactory control of die lip clearance at the time of extruding a resin from extruder, but also by thermal deformation of the lip itself and the minute difference in thickness due to pollution of lip. Even if this minute difference in thickness is under the accuracy of conventional thickness meter, it produces an upheaval on a roll because the slightly thicker parts are concentrically wound at the same position in the axial direction of winding. Although this may be preventable by lessening the length of rolling, such a means greatly lowers the yield of product. Further, if the rolling is carried out at a low tension, a shear in loosely rolled resin-coated paper takes place at the time of rolling, and the shape of resulting roll and resin coated paper surfaces are undesirably damaged.